This invention relates to the keytop of a push-button switch. More particularly, the invention relates to a push-button switch keytop, which has a small number of component parts and is capable of being reduced in size and thickness and is ideal for waterproof applications. The invention further relates to a method of manufacturing the keytop.
The reduction in the size and thickness of electronic devices that has been achieved in recent years has been accompanied by a demand to reduce the size and thickness also of the push-button switches used on the control panels of these devices.
These electronic devices include some that are used in environments in which there is the danger of humidity and moisture penetrating the interior of the device. In such case, the push-button switch also is required to have a so-called waterproof structure in which humidity and moisture will not penetrate the contact portion of the switch from the outside.
In an effort to meet these demands, a push-button switch has been proposed in which a substrate provided with a switch contact is covered with a single layer of resin film devoid of holes, a keytop comprising molding resin is placed upon the resin film and the switch contact is opened and closed via the resin film by pressing the keytop. The push-button switch having this structure is such that the resin film performs a waterproofing function to prevent water from penetrating the switch contact underlying the resin film.
However, though the above-described push-button switch has a waterproof structure, this switch requires the additional assembly step of inserting the resin film between the keytop and the switch contact, as a result of which there is a greater number of assembly steps.
Further, the keytop made of molding resin ordinarily is connected to another member (a frame) via a slender, elongated hinge, and the design is such that when the keytop is pressed, the hinge portion flexes and only the keytop recedes. However, since the keytop having this structure is provided with the hinge of a prescribed length and thickness (the hinge also is integrally molded along with the keytop and frame by means of molding resin), the extent to which the push-button switch can be reduced in size and thickness, as well as the degree to which greater integration can be achieved, diminishes correspondingly.
In order to illuminate the keytop of the push-button switch described above, a transparent material is used to manufacture the keytop and the resin film and a light-emitting element is arranged on the substrate provided with the switch contact. However, since the light emitted by the light-emitting element first passes through the resin film and then through a space at one end thereof before finally impinging upon the interior of the keytop, much of the light is lost during its travel along this path and the top side of the keytop is not illuminated efficiently.